CN112578412A - Capturing method compatible with B1C signal and B2a signal - Google Patents

Abstract

The invention provides a method for capturing a B1C signal and a B2a signal, and simultaneously capturing BOC modulation signals of various orders and QPSK signals. The double-sideband capture of the BOC signal can be realized on the premise of not increasing the resource consumption. The acquisition structure of the invention has small change and simple structure, wherein the most complicated PMF-FFT module part can directly use the traditional acquisition module, thereby reducing the task load of baseband development and debugging; the acquisition operand of the BOC signal is reduced, the double-sideband acquisition of the BOC signal is realized under the condition of unchanged resource and time consumption, and the acquisition sensitivity of the BOC signal can be effectively improved.

Description

Capturing method compatible with B1C signal and B2a signal

Technical Field

The invention relates to the field of satellite navigation, in particular to a signal acquisition method.

Background

The Beidou third generation adds a B1C signal, realizes compatibility and interoperation with a GPS L1C/Galileo E1 signal, and the B1C signal adopts a Binary Offset Carrier (BOC) modulation technology. In addition, the B1C signal is divided into data signal parts, high sensitivity carrier tracking due to no data bit hopping of the pilot signal, good pseudo correlation characteristics due to the use of layered codes, and the like, which all have a significant impact on the improvement of the positioning performance and the anti-interference performance of the future ue. However, due to the multi-peak characteristic of the autocorrelation function of the spread spectrum code brought by the BOC modulation mode, if the main peak of the autocorrelation function cannot be accurately captured, the signal cannot be stably tracked; the newly added B2a signal of the third Beidou at the same time replaces the B2I signal and is used as a new RNSS positioning frequency point. The B1C signal and the B2a signal are modulated as follows:

modulation schemes of tables 1B 1C and B2a

The problem of multi-signal compatibility must be considered in future Beidou satellite navigation receivers, especially high-precision application receivers.

Disclosure of Invention

In order to overcome the defects of the prior art, the invention provides a method for capturing a compatible B1C signal and a compatible B2a signal, and simultaneously, the method is compatible with capturing of BOC modulation signals of various orders and QPSK signals. The double-sideband capture of the BOC signal can be realized on the premise of not increasing the resource consumption.

The technical scheme adopted by the invention for solving the technical problem comprises the following steps:

the method comprises the following steps: performing AD sampling on input intermediate frequency data and performing down-conversion to zero frequency;

step two: filtering upper and lower side bands of a BOC signal, performing 2K-time reduction sampling and storing 2ms upper and lower side band data; after carrying out down-conversion on a QPSK (10) signal, carrying out K-time subtraction sampling and then storing 2ms data;

step three: storing native code data of 2ms length;

step four: for BOC signals, firstly selecting 2ms upper sideband signals and 2ms local codes to enter a PMF-FFT module for PMF-FFT operation, storing PMF-FFT results of the upper sideband, then selecting 2ms lower sideband signals and 2ms local codes to enter the PMF-FFT module, and storing PMF-FFT results of the lower sideband; for QPSK signals, 2ms of sampling data and 2ms of local codes are selected to enter a PMF-FFT module for PMF-FFT operation;

step five: for BOC signals, carrying out coherent accumulation on PMF-FFT results of upper and lower sidebands and carrying out detection judgment, and carrying out coherent accumulation on the results of the upper and lower sidebands of the BOC signals and sending the results to a detection judgment module; for QPSK signals, directly making detection decision;

when the received pseudo code is aligned with the local pseudo code, get R_U(τ)＝1，R_D(τ) ═ 1, corresponding to the code phase and doppler frequency offsets acquired.

The invention has the beneficial effects that:

1. the invention has little change on the capturing structure of the traditional QPSK signal and simple structure, wherein the most complicated PMF-FFT module part can directly use the traditional capturing module, thereby reducing the task amount of baseband development and debugging.

2. Compared with the sampling rate K times of the QPSK (10) signal, the second step of the invention utilizes the characteristic that the code rate of the B1C (BOC (1,1) modulation) signal is lower, and adopts the sampling rate 2K times, so that the acquisition computation amount of the BOC signal can be reduced, and the double-sideband acquisition of the BOC signal is realized under the condition of unchanged resource and time consumption.

3. In the fifth step of the invention, coherent accumulation is carried out on the acquisition results of the upper and lower sidebands of the BOC signal, so that the acquisition sensitivity of the BOC signal can be effectively improved.

Drawings

FIG. 1 is a conventional QPSK trapping architecture

FIG. 2 is a schematic diagram of the capture method of the invention compatible with B1C signal and B2a signal.

Detailed Description

The invention is further illustrated with reference to the following figures and examples.

The conventional QPSK signal acquisition process is shown in fig. 1.

The present invention is a method for capturing B1C signal and B2a signal, and the embodiment of the present invention is described with reference to fig. 2.

The method comprises the following steps: the input intermediate frequency data is AD sampled and down converted to zero frequency.

Without considering the influence of doppler on the code rate and the influence of data bits, the pseudo code signal model of a single satellite at the receiver is:

r(t)＝U_pD_p(t)C_p(t+τ)cos(wt+φ)+n(t)

in the formula: u shape_pTo signal amplitude, D_pFor modulated data, C_p(t + tau) is a pseudo code with a certain time delay; w-2 pi (f)_i+f_d)，f_iIs a digital intermediate frequency, f_dFor carrier Doppler shift, n (t) is band-limited white Gaussian noise with mean 0 and variance σ 2.

Step two: and filtering upper and lower sidebands of the BOC signal, performing 2K times of reduction sampling, and directly performing K times of reduction sampling on the QPSK signal.

The BOC modulation signal has a multi-peak characteristic in the autocorrelation function due to the subcarrier modulation, and the algorithm removes the multi-peak characteristic of the autocorrelation function by using a double-sideband method. Considering that the code rate of the B2a QPSK (10) signal is 10.23Mhz and the code rate of the BOC (1,1) signal is 1.023Mhz, K-times downsampling is selected for the QPSK (10) signal and 2K-times downsampling is selected for the BOC (1,1) signal. Selecting a higher down-sampling rate for the BOC (1,1) signal allows lossless unambiguous acquisition of the BOC signal without increasing time and resource consumption.

After the input signal is mixed with the local upper sideband carrier and the local lower sideband carrier, the signal model entering the matched filter bank is as follows:

in the formula, S_IU，S_QU，S_ID，S_QDThe signals are an upper sideband I signal, an upper sideband Q signal, a lower sideband I signal and a lower sideband Q signal which are subjected to sideband filtering and 2k times of reduction sampling respectively; n is_IU(t)、n_QU(t)、n_ID(t)、n_QD(t) is the noise entering the matched filter bank.

Step three: native code data of 2ms length is stored.

Native code data of 2ms length is stored for correlation with the incoming signal.

Step four: the input signal is subjected to a PMF-FFT operation.

At the receiver end, the signal-to-noise ratio needs to be improved through the pre-detection integration time, the pre-detection integration time of the whole system is set as PIT, the PIT is divided into n sections, and the integration time of each section is T-PIT/n. Let the sampling frequency be f_sThe result of the partial matched filter for the mth segment of the BOC signal is as follows:

in the formula I_U(m)、Q_U(m)、I_D(m)、Q_DAnd (m) are the correlation results of the I and Q paths of the upper and lower sidebands respectively.

T_sIs the sampling interval, R_U(τ) is the partial integration time T of the upper sideband signal_pInner code correlation value, R_D(τ) is the partial integration time T of the lower sideband signal_pThe code correlation value of inner.

Let Z (m) ═ I (m) + JQ (m) perform FFT of N (N ≧ N):

where k is 0, … …, N-1, the real and imaginary parts of the FFT are:

step five: for BOC signals, carrying out coherent accumulation on PMF-FFT results of upper and lower sidebands, carrying out detection judgment, and carrying out coherent accumulation on the results of the upper and lower sidebands of the BOC signals:

I(k)＝I_U(k)+I_D(k)

Q(k)＝Q_U(k)+Q_D(k)

a first reaction vessel I (k)²+Q(k)²Sending the data to a detection and judgment module;

for QPSK signals, directly making detection decision;

when the received pseudo code is aligned with the local pseudo code, R can be obtained_U(τ)＝1，R_D(τ) ═ 1, corresponding to the code phase and doppler frequency offsets acquired.

Claims (1)

1. A method for capturing a compatible B1C signal and B2a signal, comprising the steps of:

the method comprises the following steps: performing AD sampling on input intermediate frequency data and performing down-conversion to zero frequency;

step two: filtering upper and lower side bands of a BOC signal, performing 2K-time reduction sampling and storing 2ms upper and lower side band data; after carrying out down-conversion on the QPSK signal, carrying out K-time subtraction sampling and then storing 2ms data;

step three: storing native code data of 2ms length;

step four: for BOC signals, firstly selecting 2ms upper sideband signals and 2ms local codes to enter a PMF-FFT module for PMF-FFT operation, storing PMF-FFT results of the upper sideband, then selecting 2ms lower sideband signals and 2ms local codes to enter the PMF-FFT module, and storing PMF-FFT results of the lower sideband; for QPSK signals, 2ms of sampling data and 2ms of local codes are selected to enter a PMF-FFT module for PMF-FFT operation;

step five: for BOC signals, carrying out coherent accumulation on PMF-FFT results of upper and lower sidebands and carrying out detection judgment, and carrying out coherent accumulation on the results of the upper and lower sidebands of the BOC signals and sending the results to a detection judgment module; for QPSK signals, directly making detection decision;

when the received pseudo code is aligned with the local pseudo code, get R_U(τ)＝1，R_D(τ) ═ 1, corresponding to the code phase and doppler frequency offsets acquired.

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